This invention relates to electronic components for implantable medical devices, and more particularly implantable cardioverter/defibrillators having compact circuitry.
Implantable Cardioverter Defibrillators (ICDs) are implanted in patients susceptible to cardiac tachyarrhythmias including atrial and ventricular tachycardias and atrial and ventricular fibrillation. Such devices typically provide cardioversion or defibrillation by delivering low voltage pacing pulses or high voltage shocks to the patient""s heart, typically about 500-800V. The ICD operates by detecting a fast heart rate or tachyarrhythmia, upon which a battery within the device housing is coupled via an inverter to a high voltage capacitor or capacitor pair to charge the capacitors. When the capacitor reaches a desired voltage, charging is stopped and the capacitors are discharged under control of a microprocessor to provide a therapeutic shock to the patient""s heart.
It is desirable for ICDs to be as small as possible, primarily for patient comfort. However, it is also important to provide adequate stored energy in the device battery to allow a useful device life before surgical replacement is required. Also, device capacitors must have adequate capacitance to store and deliver a suitable charge for therapy. Advancements have permitted reductions in the size of these components. However, even for the most advanced components, there remains a desire to minimize device size.
In addition, while batteries and capacitors have traditionally been the largest device components, and therefore the primary targets for miniaturization, advancements for these components have resulted in other components having a significant effect on device size.
A ceramic hybrid is normally used for supporting the many electronic components (including integrated circuit controllers and discrete components), for connecting to the larger components such at the battery and capacitor, and for providing electrical interconnections between components. Such ceramic hybrids require significant area to mount all required components, increasing the needed area. While multi-layer boards having more than two conductive trace layers are available, these do not provide additional mounting area. In addition, even if adequate area is provided, the additional buried traces can lead to heat build-up where current flows beneath heat-generating components.
Moreover, there are disadvantages to mounting components too densely on a board even if there were adequate area. Heat generated by components can impair the function of adjacent components, or those mounted on the opposite side of the board at the same location. In ICD circuitry, certain high voltage sections of the circuit can generate parasitic capacitance, noise and interference at levels that may impair the function of low voltage circuitry immediately adjacent to or on the opposite side of the high voltage circuitry. High voltage standoff distances must be maintained to prevent arcing or shorting from one component at one potential to another at a different potential. High voltage standoff rules tend to increase the surface area that is required for a high voltage circuit.
The disclosed embodiment overcomes the limitations of the prior art by providing an implantable cardiac rhythm management device. The device has a flexible circuit sheet with a number of connected sheet portions and a number of conductive traces extending between different sheet portions. A plurality of device components are attached to the sheet, on different sheet portions. The sheet is articulated at fold lines between the sheet portions; and folded so that at least some of the sheet portions occupy different planes.